Merge changes I52ec5b02,I376656e3,I3f005583,Icba4e33d,I78400f6c, ...

* changes:
  Use PassthruPatchRecord for DIRECT to DIRECT connections
  Add PassthruPatchRecord for low latency software patches
  Abstract access to HAL stream via Source in RecordThread
  Move PlaybackThread::Track::writeFrames to PatchRecord
  audioflinger: Add tracing of buffer frames to PatchTrack/Record
  libaudioprocessing: Extract vendor-available part of AudioMixer
  AudioMixer: Cleanups
  libaudioprocessing: Trivial dependency cleanups